This is a serious affair, so please be on your best behavior. Este es un asunto serio, así que por favor compórtense adecuadamente.

I'm dead serious! Te lo digo absolutamente en serio.

seriously: en serio; gravementeadverb

Ejemplos

"No seriously, you're totally elitist."

"You've only been alive for a matter of months, but I've already had reports of public indecency, aggressive lullaby singing, diaper throwing, tummy aches, temper tantrums, loud crying and some very serious accusations of milk abuse."

"Philip : Yeah, I seriously doubt that."

"If we don't get it right, it could SERIOUSLY damage Delavigne's sales next year!"

"Philip : OK, OK, OK, seriously, first of all, I hate you guys."

"Let's get serious Jonas, how do Scandinavians spend their summers?"

"You cannot be serious!"

"But I've got to warn you, these are some pretty serious tough hombres back there."

"I'm serious!"

"At our spacious and tranquil retreat, you will find a solution for all your earthly problems. Whether you have a serious alcohol or drug addiction, a troubled marriage, or are just severely disappointed in your gay children, we have a program for you!"